pl/sql 关于层次树的部分语句不太懂
delcare
rg_id recordgroup;
begin
rg_id := create_group_from_query
('alpha','select 1, level, ename, null, to_char(empno) '
|| ' from emp where deptno= '
||:control.dno
||' connect by prior empno= mgr '
|| ' start with job=''PRESIDENT''');
v_ignore := populate_group(rg_id);
Ftree.set_tree_property(htree,Ftree.record_group,rg_id);
delete_group(rg_id);
end;
请问:每一句语句的意思?